This invention relates to a process for producing a polyester. More specifically, this invention relates to a process for polymerizing a carbonyl compound and a glycol in the presence of a coated titanium dioxide and a titanium catalyst composition.
Polyesters such as, for example, polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate, generally referred to as xe2x80x9cpolyalkylene terephthalates,xe2x80x9d are a class of important industrial polymers. They are widely used in fibers, films, and molding applications.
There are several known methods for producing polyester. In one method, polyester is produced by transesterification of an ester, such as dimethyl terephthalate, (DMT) with a glycol followed by polycondensation. In another known process, an acid such as terephthalic acid (TPA) is directly esterified with a glycol followed by polycondensation. A catalyst is typically used to catalyze the esterification, transesterification, and/or polycondensation reactions.
Antimony is often used as a catalyst for the polymerization and/or polycondensation reactions. Unfortunately, antimony-based catalysts suffer from several shortcomings. Antimony forms insoluble antimony complexes that plug fiber spinnerets. As a result, during fiber spinning, frequent shutdowns are necessary to wipe the spinnerets clean of precipitated antimony compounds. In addition, there are increased environmental and regulatory controls, especially in food contact applications, due to the toxic characteristics of antimony-based catalysts.
Titanium catalysts, which are less toxic than antimony-based catalysts, have been studied extensively for use as catalysts in these esterification, transesterification, and polycondensation reactions. Titanium catalysts reduce the amount of inorganic solids in polyester formed using antimony-based catalysts, thereby reducing pack pressure in spinning and haziness in the bottle resin. Titanium catalysts also reduce spinning breaks and improve the yield in fiber spinning.
During the production of polyester, uncoated titanium dioxide (TiO2) has been widely used as a delusterant. It has been found, however, that uncoated titanium dioxide deactivates the titanium catalyst. As a result of this deactivation, it becomes necessary to dramatically increase the amount of titanium catalyst to achieve the same degree of polymerization as the amount of titanium catalyst used without a titanium dioxide delusterant.
There is a need for a new process for producing polyester wherein the degree of deactivation of the titanium catalyst caused by titanium dioxide is reduced or eliminated.
The present invention provides a process for producing a polyester, wherein deactivation of the titanium catalyst by a titanium dioxide is reduced or eliminated.
The present invention provides a process for producing a polyester. The process comprises polymerizing a polymerization mixture comprising (i) a carbonyl compound or an oligomer of a carbonyl compound and (ii) a glycol, in the presence of a titanium catalyst composition, to produce the polyester, wherein a coated titanium dioxide comprising a titanium dioxide and a coat is added before or during the polymerizing.
The coat of the coated titanium dioxide can comprise an aluminum compound, a silicon compound, a manganese compound, a phosphorous compound, an antimony compound, a cobalt compound, an organic compound, or a combination thereof. In one embodiment, the coat comprises at least one of an aluminum oxide, a silicon oxide, a potassium oxide, an antimony oxide, or a manganese oxide. In another embodiment, the coat comprises polyethylene oxide, trimethylolpropane, polyvinylpyrrolidone, polyvinyl alcohol, or a combination of two or more thereof.
In one embodiment, the titanium dioxide is 70 to 99.5% by weight of the coated titanium dioxide. In another embodiment, the coat is 0.5 to 30% by weight of the coated titanium dioxide.
The invention provides a process for producing a polyester which comprises polymerizing a polymerization mixture comprising (i) a carbonyl compound or an oligomer of said carbonyl compound and (ii) a glycol, in the presence of a titanium catalyst composition, to produce said polyester. In the process of the invention, a coated titanium dioxide comprising titanium dioxide and a coat is added before or during the polymerizing.
The coated titanium dioxide of the invention comprises a coat and titanium dioxide. The titanium dioxide can be anatase or rutile, and is partially or completely coated with the coat. The coat is made of an organic and/or an inorganic material. Suitable coating materials include, but are not limited to, an aluminum compound, a silicon compound, a manganese compound, a phosphorous compound, an antimony compound, a cobalt compound, an organic compound such as polyethylene oxide and/or trimethylolpropane, and combinations of two or more thereof. Preferably, the coat is 0.5 to 30% by weight of the coated titanium dioxide, more preferably 2 to 20% by weight, and most preferably 3 to 10% by weight.
Examples of coating compounds include, but are not limited to, an aluminum oxide, a silicon oxide, a potassium oxide, an antimony oxide, a manganese oxide, polyethylene oxide, and trimethylolpropane. The coat of the coated titanium dioxide is 0.5% to 30% by weight of the coated titanium dioxide.
In one embodiment, the coat of the coated titanium dioxide comprises one or more of the following, such that the coat of the coated titanium dioxide is 0.5% to 30% by weight of the coated titanium dioxide: (i) 0.01% to 10% Al2O3, preferably 0.01% to 5%; (ii) 0.01 to 20% SiO2, preferably 0.01 to 10%; (iii) 0.01 to 2% P2O5, preferably 0.01 to 1%; (iv) 0.01 to 1% Sb2O3; (v) 0.01 to 1% MnO; (vi) 0.01 to 20% of an organic compound such as polyethylene oxide or trimethylolpropane, preferably 0.01 to 5%.
The coated titanium dioxide can be in the form of a slurry that comprises coated titanium dioxide in a glycol and/or water. The concentration of coated titanium dioxide in the slurry can be 1 to 80%, preferably 10 to 60%, most preferably 20 to 30% by weight.
In one embodiment, the coated titanium dioxide slurry includes a glycol having 1 to 10, preferably 1 to 8, and most preferably 1 to 4 carbon atoms per molecule, such as an alkylene glycol, a polyalkylene glycol, an alkoxylated glycol, or combinations thereof. Examples of suitable glycols include, but are not limited to, ethylene glycol, propylene glycol, isopropylene glycol, butylene glycol, 1-methyl propylene glycol, pentylene glycol, diethylene glycol, triethylene glycol, polyoxyethylene glycol, polyoxypropylene glycol, polyoxybutylene glycol and combinations of two or more thereof. The most preferred glycols are ethylene glycol, 1,3-propanediol, and butylene glycol, which can be used in the production of commercially important polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate.
The slurry of coated titanium dioxide can be prepared using techniques well known to those skilled in the art. The slurry can be prepared in any suitable vessel or container by techniques well known to those skilled in the art, such as wet milling, sand milling, pearl milling, ball milling, colloid milling, homogenization, centrifugation, agitation, filtration, and combinations of two or more thereof.
Optionally, the coated titanium dioxide slurry can further include a dispersing agent. The coated titanium dioxide can be mixed in the presence of a dispersing agent, such as potassium tripolyphosphate, potassium pyrophosphate, polyvinylpyrrolidone, and/or polyvinyl alcohol, with a glycol to form a slurry.
Examples of suitable dispersing compounds include, but are not limited to, a polyphosphoric acid or a salt thereof, a phosphonate ester, a pyrophosphoric acid or salt thereof, a pyrophosphorous acid or salt thereof, polyvinylpyrrolidone, polyvinyl alcohol, and combinations of two or more thereof. The polyphosphoric acid can have the formula of Hn+2PnO3n+1 in which n is xe2x89xa72. The phosphonate ester is selected from the group consisting of (R1O)2P(O)ZCO2R1, di(polyoxyethylene) hydroxymethyl phosphonate, and combinations thereof; wherein each R1 is independently selected from hydrogen, a C1-4 alkyl, and combinations thereof; and Z is selected from a C1-5 alkylene, a C1-5 alkylidene, and combinations thereof. Presently preferred dispersing agents include potassium tripolyphosphate, potassium pyrophosphate, and triethyl phosphonoacetate.
The coated titanium dioxide slurry can be made in a batch process that is simple and inexpensive to operate. The slurry can also be carried out by continuous methods which are well known to one skilled in the art.
In one embodiment, the quantity of the coated titanium dioxide that is added to the polymerization mixture is 0.001 to 10 weight %, preferably 0.03 to 2.0 weight % of the polymerization mixture. The coated titanium dioxide can be added before, during, or after the esterification or transesterification process of the carbonyl compound or the oligomer of the carbonyl compound. The coated titanium dioxide can also be added before or during the polycondensation of the carbonyl compound or the oligomer of the carbonyl compound.
The titanium catalyst composition used in the process of the invention can be any of those titanium catalysts conventionally used to produce a polyester. The titanium catalyst composition can be in a solid form, or the titanium catalyst composition can be a slurry or solution that further comprises glycol and/or water.
In one embodiment, the titanium catalyst composition comprises a tetraalkyl titanate, also referred to as a titanium tetrahydrocarbyloxide, which is readily available. Examples of suitable tetraalkyl titanates include those having the formula of Ti(OR)4, wherein each R is individually selected from an alkyl, cycloalkyl, alkaryl, hydrocarbyl radical containing from 1 to about 30, preferably 2 to about 18, and most preferably 2 to 12 carbon atoms per radical. Titanium tetrahydrocarbyloxides in which the hydrocarboxyl group contains from 2 to about 12 carbon atoms per radical which is a linear or branched alkyl radical are preferred because they are relatively inexpensive, more readily available, and effective in forming the solution. Suitable tetraalkyl titanates include, but are not limited to, titanium tetraethoxide, titanium tetrapropoxide, titanium tetraisopropoxide, titanium tetra-n-butoxide, titanium tetrahexoxide, titanium tetra 2-ethylhexoxide, titanium tetraoctoxide, and combinations of two or more thereof. The titanium tetrahydrocarbyloxides are well known to one skilled in the art and are provided, for example, in U.S. Pat. Nos. 6,066,714 and 6,166,170, the descriptions of which are incorporated herein by reference. Examples of commercially available organic titanium compounds include, but are not limited to, TYZOR(copyright) TPT and TYZOR(copyright) TBT (tetra isopropyl titanate and tetra n-butyl titanate, respectively) available from E. I. du Pont de Nemours and Company, Wilmington, Del., U.S.A.
The titanium catalyst composition can also comprise titanium glycolate, optionally in the presence of water. Titanium glycolate can be produced by contacting a titanium compound, such as tetraisopropyl titanate, with an alkyl glycol, such as ethylene glycol, 1,3-propanediol, or butylene glycol. The catalyst composition can also be a titanic acid having the formula H2TiO3, TiO(OH)2, or TiO2.H2O, titanium dioxide, or combinations thereof.
According to an embodiment of the invention, the esterification, transesterification, or polymerization process can comprise contacting, optionally in the presence of a phosphorus compound and/or a cocatalyst, either (a) a titanium catalyst composition and a coated titanium dioxide slurry in a first glycol and/or water with a polymerization mixture comprising a carbonyl compound and a second glycol or (b) a titanium catalyst composition and a coated titanium dioxide slurry in a first glycol and/or water with an oligomer derived from a carbonyl compound and a second glycol under a condition effective to produce a polymer comprising repeat units derived from the carbonyl compound or its ester, first glycol, and second glycol. The second glycol can be the same or different from the first glycol. The presently preferred second glycol is ethylene glycol, 1,3-propanediol (propylene glycol), butylene glycol, or a combination of two or more thereof.
In the process of the invention, the titanium catalyst composition can be used as a polycondensation catalyst. Alternatively, the titanium catalyst composition can be present in the ester exchanger to accelerate the transesterification reaction or in the esterifier to accelerate the esterification reaction. Generally, the titanium catalyst composition is more active in the polycondensation reaction than the esterification or transesterification reactions. The proper level of titanium catalyst composition for esterification or transesterification can be an excess level for polycondensation. When titanium catalyst composition present in the esterifier or ester exchanger (transesterifier) is an excess for polycondensation, or when polycondensation is intended with a non-titanium catalyst such as antimony, part of or all of the titanium catalyst is preferably deactivated or inhibited after esterification or transesterification with a phosphorus compound to avoid discoloration of the polymer.
The titanium catalyst composition can further include a cocatalyst present in the range of about 0.001 to about 30,000 ppm by weight of the polymerization mixture comprising the carbonyl compound and glycol, preferably about 0.1 to about 1,000 ppm by weight, and most preferably 1 to 100 ppm by weight. Suitable cocatalysts include, for example, a cobalt cocatalyst, an aluminum cocatalyst, an antimony cocatalyst, a manganese cocatalyst, a zinc cocatalyst, or a combination of two or more thereof. Such cocatalysts are well known to those skilled in the art. In another embodiment, the cocatalyst comprises a cobalt/aluminum cocatalyst. Cobalt/aluminum catalysts comprise a cobalt salt and an aluminum compound, in which the mole ratio of aluminum to cobalt salt is in the range of from 0.25:1 to 16:1. Cobalt/aluminum catalysts are disclosed in U.S. Pat. No. 5,674,801, the disclosure of which is incorporated herein by reference. When a cocatalyst is present in the process of the invention, the cocatalyst can either be separate from or can be included as part of the titanium catalyst composition.
The titanium catalyst composition can also include additives which are well known in the art. For example, the titanium catalyst composition can include a stabilizer (i.e., a substance that prevents the titanium catalyst composition solution from gelling or precipitating), such as a phosphorous stabilizer compound, and/or a toner compound, such as a cobalt toner compound.
The titanium catalyst present in the polyester can cause increased degradation and yellowness in future processing. To reduce and/or eliminate degradation and yellowness in future processing, part or all of the titanium catalyst can be deactivated or inhibited after polymerization with a phosphorus compound to avoid discoloration of the polymer. Similarly, when manganese, zinc, cobalt, or other catalysts are used as an esterification or transesterification catalyst and the titanium catalyst is used as a polycondensation catalyst, these catalysts can be deactivated by the presence of a phosphorus compound. Accordingly, the titanium catalyst composition can also include a phosphorus compound.
Any phosphorus compound that can stabilize a titanium-glycol solution (i.e., can prevent the solution from gelling or precipitating) can be used to deactivate the catalyst. Examples of suitable phosphorus compounds include, but are not limited to, a polyphosphoric acid or a salt thereof, a phosphonate ester, a pyrophosphoric acid or salt thereof, a pyrophosphorous acid or salt thereof, and combinations of two or more thereof. The polyphosphoric acid can have the formula of Hn+2PnO3n+1 in which n is xe2x89xa72. The phosphonate ester can have the formula of (R2O)2P(O)ZCO2R2 in which each R2 can be independently hydrogen, a C1-4 alkyl, or a combination thereof; and Z is a C1-5 alkylene, a C1-5 alkylidene, or combinations thereof, di(polyoxyethylene) hydroxymethyl phosphonate, and combinations of two or more thereof. The salt can be an alkali metal salt, alkaline earth metal salt, ammonium salt, or a combination of two or more thereof.
Illustrative examples of suitable phosphorus compounds include, but are not limited to, potassium tripolyphosphate, sodium tripolyphosphate, potassium tetra phosphate, sodium pentapolyphosphate, sodium hexapolyphosphate, potassium pyrophosphate, potassium pyrophosphite, sodium pyrophosphate, sodium pyrophosphate decahydrate, sodium pyrophosphite, ethyl phosphonate, propyl phosphonate, hydroxymethyl phosphonate, di(polyoxyethylene) hydroxymethyl phosphonate, methylphosphonoacetate, ethyl methylphosphonoacetate, methyl ethylphosphonoacetate, ethyl ethylphosphonoacetate, propyl dimethylphosphonoacetate, methyl diethylphosphonoacetate, triethyl phosphonoacetate, and combinations of two or more thereof.
In one embodiment, the titanium catalyst composition comprises a salt of a polyphosphoric acid having 0.001% to 10% by weight titanium, 50% to 99.999% by weight glycol, and 0% to 50% by weight water, in which the molar ratio of phosphorus to titanium is about 0.001:1 to 10:1.
According to the invention, a phosphorus compound can be present in the process before, during, or after the carbonyl compound or oligomer of the carbonyl compound is esterified or transesterified. Similarly, the phosphorous compound can be present before, during, or after polycondensation.
Any carbonyl compound which, when combined with a glycol, can produce a polyester can be used. Such carbonyl compounds include, but are not limited to, acids, esters, amides, acid anhydrides, acid halides, salts of carboxylic acid, oligomers or polymers having repeat units derived from an acid, or combinations of two or more thereof. The presently preferred acid is an organic acid such as a carboxylic acid or ester thereof. The oligomer of a carbonyl compound such as terephthalic acid and glycol generally has a total of about 2 to about 100 repeat units, preferably from about 2 to about 20 repeat units, derived from the carbonyl compound and glycol. The oligomer of the carbonyl compound, such as terephthalic acid, can be produced by contacting terephthalic acid, its ester, or combinations thereof with a second glycol under esterification, transesterification, or polymerization conditions well known to one skilled in the art to produce a total of about 2 to about 100, preferably from about 2 to about 20 repeat units derived from the terephthalic acid and glycol.
The organic acid or ester thereof can have the formula of R2O2CACO2R2 in which each R2 independently can be (1) hydrogen or (2) a hydrocarbyl radical in which each radical has 1 to about 30, preferably about 3 to about 15 carbon atoms per radical which can be alkyl, alkenyl, aryl, alkaryl, aralkyl radical, or combinations of two or more thereof, and in which A is an alkylene group, an arylene group, alkenylene group, or combinations of two or more thereof. Each A has about 2 to about 30, preferably about 3 to about 25, more preferably about 4 to about 20, and most preferably 4 to 15 carbon atoms per group. Examples of suitable organic acids include, but are not limited to, terephthalic acid, isophthalic acid, napthalic acid, succinic acid, adipic acid, phthalic acid, glutaric acid, oxalic acid, and combinations of two or more thereof. Examples of suitable esters include, but are not limited to, dimethyl adipate, dimethyl phthalate, dimethyl terephthalate, dimethyl glutarate, and combinations of two or more thereof. The preferred organic acid is terephthalic acid or its ester dimethyl terephthalate.
The molar ratio of the glycol to carbonyl compound is selected to effect the production of an ester or polyester. Generally, the ratio of glycol to carbonyl can be in the range of from about 1:1 to about 10:1, preferably about 1:1 to about 5:1, and most preferably 1:1 to 4:1.
In one embodiment, the polyester is produced in a temperature in the range of from about 150xc2x0 C. to about 500xc2x0 C., preferably about 200xc2x0 C. to about 400xc2x0 C., and most preferably 250xc2x0 C. to 300xc2x0 C. under a pressure in the range of from about 0.001 to about 1 atmosphere (0.1 to 101.3 kPa) for a time period of from about 0.2 to about 20, preferably about 0.3 to about 15, and most preferably 0.5 to 10 hours.
The process of the invention can also be carried out using any of the conventional melt or solid state techniques and in the presence or absence of a toner compound to reduce the color of a polyester produced. Examples of toner compounds include, but are not limited to, cobalt aluminate, cobalt acetate, Carbazole violet (commercially available from Hoechst-Celanese, Coventry, R.I., U.S.A., or from Sun Chemical Corp, Cincinnati, Ohio, U.S.A.), Estofil Blue S-RLS and Solvent Blue 45TM (from Sandoz Chemicals, Charlotte, N.C., U.S.A), CuPc Blue (from Sun Chemical Corp, Cincinnati, Ohio, U.S.A.). These toner compounds are well known to one skilled in the art and the description of which is omitted herein. The toner compound can be used with the catalyst disclosed herein in the amount of about 0.1 ppm to 1000 ppm, preferably about 1 ppm to about 100 ppm, based on the weight of polyester produced.
The invention process can also be carried out using any of the conventional melt or solid state techniques and in the presence or absence of an optical brightening compound to reduce the yellowness of the polyester produced. Examples of optical brightening compounds include, but are not limited to, 7-naphthotriazinyl-3-phenylcoumarin (LEUCOPURE EGM, from Sandoz Chemicals, Charlotte, N.C., U.S.A.), 4,4xe2x80x2-bis(2-benzoxazolyl) stilbene (EASTOBRITE, from Eastman Chemical, Kingsport, Tenn., U.S.A.). These optical brightening compounds are well known to one skilled in the art and the description of which is omitted herein. The optical brightening compound can be used with the catalysts disclosed herein in the amount of about 0.1 ppm to 10,000 ppm, preferably about 1 ppm to about 1000 ppm, based on the weight of polyester produced.